The present invention relates to a process for the production of pure hydrogen from a gas such as natural gas, containing helium. It relates more specifically to a process permitting producing hydrogen of satisfactory purity for use in electronic sector.
It also relates to an installation for the practice of this process.
Among the various known processes in this field, one of the conventional methods to produce hydrogen of high purity consists in carrying out a steam reforming of hydrocarbons followed by a catalytic conversion with steam, of the carbon monoxide present in the gaseous mixture obtained. The resulting synthesis gas is then purified in a PSA (Pressure Swing Adsorption) unit.
The source of these hydrocarbons is generally a natural gas network which contains methane and other heavy hydrocarbons but also sulfur compounds, nitrogen, carbon dioxide and helium.
Most of these impurities can be eliminated in the course of the production and purification process for hydrogen, except helium, which is an inert chemical compound. The latter is generally present in an amount of 100 to 1000 ppm and has a low adsorptive power, such that this element is found almost necessarily in the produced purified hydrogen.
This impurity is not generally troublesome in most uses of hydrogen purified by this type of process.
However, in the electronic field, it is necessary to have very high purity hydrogen and it thus becomes desirable to produce hydrogen containing no helium.
At present, to produce hydrogen free from helium, there is generally used a primary material not containing this impurity. There can thus be provided a steam reforming process as mentioned, from naphtha or methanol. These however are semi-finished products and the cost of this primary material is fairly high. Another route is the production of hydrogen by electrolysis of water. However this requires high energy and is used essentially for small scale production of purified hydrogen.
From the point of view of the separation of the helium contained in hydrogen, the means available in the art are limited either to liquefaction of the natural gas by cryogenic processing, or the use of metallic membranes such as palladium membranes downstream of a PSA unit, the use of such membranes supposing the availability of a product that has already preliminarily been purified. As a result, the separation of helium present in hydrogen remains very difficult and costly until now.
The object of the present invention is to provide a process permitting producing very high purity hydrogen, in particular containing no helium.
Another object of the present invention is to provide such a process using a gas which contains helium, as a starting material, in particular natural gas.
Another object of the invention is again to provide such a process that will be relatively simple and inexpensive.
The object of the present invention is also to provide an installation for practicing such a process.
These objectives as well as others which will become apparent in the light of the description which follows, are achieved by means of a process for the production of high purity hydrogen, substantially free from helium, from a feed gas containing essentially hydrocarbons, particularly methane, and impurities including helium, of the type comprising the conversion of the hydrocarbons, particularly the methane, into hydrogen and carbon dioxide, and the purification in a PSA unit of the hydrogen contained in the resulting gaseous mixture, characterized in that, prior to conversion of the hydrocarbons, particularly methane, the feed gas is processed in a unit for separation by permeation, producing a retentate gas impoverished in helium, containing essentially hydrocarbons, particularly methane, and a permeate gas enriched in helium, said retentate gas being then processed in said hydrocarbon conversion unit, particularly as to methane, by producing a gaseous mixture practically free from helium, containing hydrogen.
According to other characteristics of the invention:
the feed gas is a natural gas containing helium, particularly between 100 and 1000 ppm helium;
the conversion of the hydrocarbons, particularly the methane, contained in the retentate gas impoverished in helium, is carried out by steam reforming, then catalytic conversion with steam of the carbon monoxide product into carbon dioxide;
a portion of the feed gas is used as an energy source for the burners producing the heat necessary for the steam reforming operation;
the residual low pressure gaseous permeate from the unit of separation by permeation is used as an energy source for the burners producing the heat necessary for the steam reforming operation;
the residual gas from the PSA purification unit is used as a source of energy for the burners producing the heat necessary for the steam reforming operation;
the conversion of the hydrocarbons, particularly the methane, contained in the retentate gas impoverished in helium, is carried out by partial oxidation;
the low pressure residual permeate gas from the unit of separation by permeation and/or the residual gas from the PSA unit, are used as energy source to produce the steam in an auxiliary heater.
The invention also has for its object an installation for the production of high purity hydrogen, substantially free from helium, from a feed gas containing hydrocarbons, particularly methane and impurities including helium, of the type comprising a unit comprising conversion means for the hydrocarbons, particularly the methane, into hydrogen and carbon dioxide, and a unit for purification by modulated pressure adsorption or PSA, of the hydrogen contained in the resulting gaseous mixture, characterized in that it moreover comprises, upstream of said hydrocarbon conversion means, particularly the methane, a unit for separation by permeation, means for supplying feed gas to said permeation unit, and means for supplying retentate gas produced in the unit for separation by permeation, to said hydrocarbon conversion means, particularly for the methane.